This application claims the benefit of co-pending German Patent Application No. 100 02 583.8-34 entitled xe2x80x9cVorrichtung zur unterbrechungsfreien Stromversorgung einer elektrischen Last mit Wechselstromxe2x80x9d, filed on Jan. 21, 2000.
The present invention generally relates to an apparatus for uninterruptedly supplying power as alternating current to an electrical load. Under normal conditions, the electrical load is supplied with power by an external source of power, for example by a public network. It is common practice in the art to also call such an apparatus an UPS.
Apparatuses for uninterruptedly supplying power as alternating current to an electrical load are commonly known in the art. The known apparatuses control an output voltage being supplied to the electrical load not only in case of trouble conditions, but also during normal conditions when the electrical load is supplied with power by a public network or by a different external source of power. This is the case in the product xe2x80x9cUNIBLOCKxe2x80x9d of Piller GmbH, Osterode am Harz, Germany. xe2x80x9cUNIBLOCKxe2x80x9d includes an electrical machine having a separate engine winding and a generator winding or coil. The engine winding of the electrical machine is used as a drive. Under normal conditions, the machine is fed by the external source of power. Under trouble conditions, the machine is fed by a battery, for example. An inverter is arranged after the battery. A combustion engine directly driving the electrical machine may be arranged to compensate for rather long breakdowns of the power supply by the external source of power. The output voltage for the electrical load may be taken from the generator winding of the electrical machine. The output voltage almost has the form or shape of an ideal sine even in case of varying input voltage or varying output current. This fact results from the construction of the electrical machine including a special dampening cage. The known product xe2x80x9cUNIBLOCKxe2x80x9d has the disadvantage of the special electrical machine being rather complicated and expensive.
It is also known in UPS systems to connect a substitute power supply device for the trouble conditions to a coupling choke at the side of the load. The coupling choke is arranged between the load and the external source of power. The coupling choke prevents the current from flowing into a current network breaking down before a fast-opening switch may be opened. Usually, the fast-opening switch is arranged at the side of the source in front of the coupling choke. The coupling choke at least prevents great short circuit currents with respect to the current network.
It is also known in the art that a substitute storage device for electrical energy in a UPS may include different sources of energy typically providing direct current becoming inverted to alternating current by an inverter.
Briefly described, the present invention provides an apparatus for uninterruptedly supplying power as alternating current to an electrical load being supplied with power by an external source of power during normal conditions.
The apparatus includes a coupling choke being operably arranged between the electrical load and the external source of power. A generator is operably connected to the coupling choke on the side of the electrical load, and it is designed and arranged to be active during normal conditions and during trouble conditions. Trouble conditions are to be understood as conditions when the external source of power fails. A converter is operably connected to the coupling choke. A substitute storage device for electrical energy is operably connected to the coupling choke on the side of the electrical load by the converter. A fast-opening switch is operably connected the coupling choke on the side of the source of power, and it is designed and arranged to open in case of occurring trouble conditions. A first unit is designed and arranged to sense an output voltage being supplied to the electrical load and to produce a measuring signal. A second unit is designed and arranged to control the output voltage, to use the measuring signal as an input signal, to deliver a control signal as an output signal to the converter and to control the output voltage to a desired shape over time.
The present invention also relates to an uninterruptible power supply system (UPS). The system includes a coupling choke being operably arranged between an external source of power and an electrical load to be supplied with power by the external source of power during normal conditions. A generator is operably connected to the coupling choke. The generator is constructed and placed to be active during normal conditions as well as during trouble conditions meaning conditions when the external source of power fails. A converter is operably connected to the coupling choke. A substitute storage for electrical energy is operably connected to the coupling choke via the converter. A switch is operably connected the coupling choke. The switch is constructed and arranged to open quickly in case of occurring trouble conditions. A first unit is designed and arranged to sense an output voltage being supplied to the electrical load and to produce a measuring signal. A second unit is designed and arranged to control the output voltage or electric potential, to use the measuring signal as an input signal, to send a control signal as an output signal to the converter and to control the output voltage to attain a certain desired shape over time.
The novel UPS system combines the advantages of a static system, especially a fast control of the voltage, with the advantages of a rotating system, especially a great short circuit power. The novel UPS system includes a standard generator. The standard generator is connected to the coupling choke in shunt Standard generators of different power are sold at a low price. The one winding or coil of the generator is used as engine winding and, simultaneously, as generator winding. During normal conditions as well as during trouble conditions, the generator provides the output voltage being supplied to the load and the idle power being required by the respective load. During normal conditions the effective power for the load is supplied by the external source of power. Usually, the external source of power is the public network. During trouble conditions, the load is supplied with effective power by the substitute storage device for electrical energy via the converter. During trouble conditions, a first unit being constructed and placed to control the output voltage controls the converter in response to a measuring signal by a control signal in a way that the output voltage being supplied to the load has the value over time. The at least one first unit being designed and arranged to control the output voltage may be a control device. The measuring signal is produced by at least one second unit being constructed and placed to sense and determine the output voltage. The unit being designed and arranged to sense the output voltage may be a voltage sensor. Usually, it is desired to achieve a sinusoidal shape of the output voltage.
It is advantageous if the unit for controlling the output voltage controls the value of the output voltage over time to reach the desired form in response to the output signal of the unit for sensing the output voltage even when the external source of power does not fail. In this way, the converter helps to improve the quality of the power supply also during normal conditions. The converter has an effect on the output voltage during each variation of the value over time being different from the ideal shape.
It is to be understood that the converter of the novel UPS is a unit being capable of reacting quickly to undesired variations of the output voltage clue to the control signal. Thus, it is especially desired that the converter is an IGBT converter. It is known in the art that IGBT stands for xe2x80x9cIsolated Gate Bipolar Transistorxe2x80x9d meaning a certain semiconductor technology being suitable for the field of power electronics.
It is no problem and it is known in the art to design the unit for controlling the output voltage, preferable the control unit, to be sufficiently fast.
A combustion engine for directly driving the generator during trouble conditions may serve to compensate for rather long breakdowns of the external source of power. Preferably, the combustion engine is coupled to the generator by an overunning clutch. In this way, the combustion engine may be started without having a negative influence on the generator, and it starts to drive the generator after having reached its nominal number of revolutions. It is not necessary to control a separate coupling movement of the active combustion engine to the generator.
The substitute storage device for electrical energy supplying the converter of the novel UPS with power includes at least one source of energy supplying direct current or alternating current. The source of energy supplying direct current may include a super conductive magnetic energy storage device (SMES), a super capacity, a battery or a fuel cell. The source of energy supplying alternating current may include a generator including a rotating centrifugal mass. A converter may be arranged in front of the generator. In this way, the generator may be arranged to be parallel to possible sources of energy supplying direct current.
A transformer may be arranged between the load and the converter being controlled by the unit for controlling the output voltage. Preferably, the transformer is also arranged between the generator and the converter. Using an IGBT converter, a load may be supplied with an output voltage in the medium voltage range, and the respective output voltage may be controlled to attain the desired form. The generator may be designed as a usual standard generator being directly applicable in the medium voltage range. This fact is an outstanding advantage compared to special electrical machines usually not being available for this voltage range.
As it is already known in the art, the coupling choke may also be partly arranged between the generator and the converter, on the one hand, and the load, on the other hand to prevent the generator and the converter, respectively, from being subject to great short circuit currents in the region of the load.